A driving control technique for a vehicle is well known. For example, a road shape, on which the vehicle runs, is estimated. Warning information is noticed based on comparison between the estimated road shape and actual driving trajectory of the vehicle. JP-B-3720117 teaches that a device includes two CCD cameras and a stereo image processor. Two cameras are arranged on right and left sides of the vehicle, respectively. Two cameras shoot scenery and/or an object in front of the vehicle in a stereo manner so that the cameras output image signals. The image signals are processed by a triangulation method with a stereo method so that a distance to the scenery and the object is calculated. Thus, a distance image showing a three-dimensional distance distribution of the scenery and the object is formed on a whole screen. Thus, a three-dimensional shape of a road or the like is detected. Based on the road shape and an actual speed of the vehicle, the device estimates possibility to drive out from a lane of the road attributed to excessive speed before the vehicle reaches a curve of the road. If necessary, the device notices warning to a driver of the vehicle.
In the above technique, it is necessary to use two CCD cameras and the stereo image processor. Therefore, the construction of the device is complicated. Further, a process executed in the device is also complicated.
Further, JP-B-3432881 teaches that a road shape is determined based on a road map, and a turning angle of a steering wheel is controlled based on the determined road shape. The road map includes a set of coordinates of multiple nodes.
In the above technique, error of a current position of the vehicle, which is detected by a navigation device, or deficient accuracy of map information may not provide optimum control of a steering wheel angle corresponding to actual road shape.